The tragic events connected with Japan's devastating earthquake and tsunami have been compounded by the threat of major nuclear contamination, most especially the possibility of a meltdown in the Fukushima No. 1 nuclear power plant. Japanese authorities have evacuated 200,000 neighbors of that plant to protect them from radiation exposure should a full meltdown occur. The events unfolding in northern Japan certainly have created global concern, including needless health anxiety among friends and patients in Los Angeles, as the situation conjures up memories of the 1986, Soviet-era Chernobyl nuclear reactor meltdown that killed dozens. That catastrophe resulted in the release of a cloud of nuclear toxins, especially radioactive iodine, which the winds carried for hundreds of miles, contaminating a large area. This led to a hundred-fold increase in thyroid cancer in children and adolescents in the Belarus and Ukraine regions. Most of the radioactive iodine was inhaled; some was ingested from contaminated produce and from milk produced by cows feeding on contaminated grass.

The thyroid, the butterfly shaped gland beneath the Adam's apple in the neck, requires iodine to make thyroid hormone, which is needed to maintain normal metabolism. The iodine is absorbed from the diet, enters the bloodstream and is concentrated in the thyroid. Thus, radioactive iodine also will concentrate in the thyroid and can damage DNA in thyroid cells. This can lead to the formation of benign and malignant thyroid nodules. Infants and children are the most susceptible to radioactive iodine's harm, because their thyroid cells actively are dividing as kids grow. Adults are relatively resistant to tumor-causing effects of radioactive iodine.

The best way to protect the thyroid from radioactive iodine's damage is to prevent exposure in the first place through evacuation or "in-place" sheltering. Another effective way is to administer potassium iodide (KI). The iodine in KI competes with the radioactive iodine for uptake by the thyroid gland. The more "cold" iodide given in the form of KI, the less radioactive iodine that can be taken up by the thyroid. The effectiveness of KI in protecting the thyroid gland was demonstrated by Poland in the Chernobyl crisis. Polish authorities administered it to half a million children younger than 16 and 17 million adults. Poles, despite their Chernobyl-related exposure to radioactive iodine, recorded no increase in thyroid cancer.

In the United States, the history of KI treatment, discussed since the 1950s Pacific atoll nuclear tests, has been fraught with missteps, including a flawed attempt to deploy the therapy after the Three Mile Island accident in 1979. By 2001, the Nuclear Regulatory Commission had issued a guidance to the States that they should consider KI to protect the public within a 10-mile radius of commercial nuclear power plants. That same year the FDA published a guidance, "Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies," in which regulators suggested that infants from birth to 1 month should receive 16 mg of KI; between 1 month and 3 years, 32 mg; and children ages 3-12, 65mg of KI. Youths from ages 12 to 18, the FDA said, also should receive a 65 mg dose, unless they are close to adult size, in which case they should receive adult-recommended 130 mg. Those older than 40 should receive KI only on the release of a very large amount of radioactive iodine because they're far less likely to develop problems from it. Pregnant and lactating women should receive at least a single dose of the KI. Potassium iodine protects the thyroid for 24 hours and generally only one to two doses would be required. The anticipated risk of further exposure decreases rapidly as the radioactive cloud disperses. Potassium iodide is available over-the-counter and is usually distributed by local authorities free of charge to residents living in proximity to a nuclear reactor. It stays good for at least five years. It is best taken 6-12 hours before exposure, but will have some efficiency if taken up to four hours after exposure. KI will not protect against the often deadly harm of other radioisotopes released in a meltdown

There are few side-effects to KI and generally they are mild. The Polish experience indicates the most frequent complaint is gastrointestinal distress, especially among children, which was primarily due to the bad taste of KI. The taste can be disguised by crushing a tablet and putting it into raspberry syrup, low-fat chocolate milk or orange juice. About 1% of children and adolescents develop a rash. Other potential risks include allergic reaction to the iodine, which is rare, and irritation of the salivary glands. Those with a history of iodine sensitivity, dermatitis herpetiformis or vasculitis should not take KI. Individuals with multinodular goiters may develop hyperthyroidism and patients with Graves' disease, an autoimmune process that leads to hyperthyroidism, may experience a worsening of their condition. Also, people with autoimmune thyroid disease may develop hypothyroidism when given a large dose of iodide. In the Polish experience, less than a half percent of newborns developed transient hypothyroidism. Though of concern because of the need for thyroid hormone for normal brain development, it did not appear to harm the infants with this transient thyroid problem.

I have received numerous calls from patients and friends worried that Japan's nuclear power plant woes will release a cloud of radioactive iodine that will affect us on the West Coast. Though events continue to develop, this would be most unlikely to occur. The Fukushima No. 1 power station has significantly better safety systems than did Chernobyl, and even if there were a total coolant failure, there will be much less radiation released than in 1986. Japanese authorities also acted rapidly to take control of their situation, again minimizing the major environmental risk. Finally, the distance between Japan and the West Coast is so large, the risk of a significant increase in radiation being detected here is very low. So, while it is nice to be prepared with information, I would not suggest running out to stock up on KI at this time.